gistfile1.ml

(* Take 2 lists, return a tuple with the elements that are in both and the    *)
(* elements that are only in first list, and elements only in second list     *)
let list_diff l1 l2 =
  let (shared, only_in_first) = List.fold_left
    (fun (s, o) e -> if List.mem e l2 then (e::s, o) else (s, e::no))
    ([], []) l1 in
  let only_in_second = List.fold_left
    (fun o e -> if List.mem e shared then o else e::o) [] l2 in
  (shared, only_in_first, only_in_second)